86 A MONOGRAPH Of THE 



thin slices at right angles to the surface, but could not 

 detect in the dermal crust anything in the shape of oscula 

 or intermarginal cavities. At the same time, I believe 

 MM. Adouin and Milne-Edwards's observations to be per- 

 fectly correct, and especially so as we are now avrare that 

 in Hyineniacedon caruncula and Spongilla fluviatilis, the 

 oscula are opened and closed in precisely the manner de- 

 scribed by those authors, and in the latter genus the poreS 

 have also the same power of opening at the will of the 

 animal ; and that when in a closed condition, no indication 

 of their presence is visible in the dermal membrane. A 

 portion of the spicula of the skeleton become external 

 defensive ones, being intermixed with the defensive fasciculi. 

 The true defensive spicula, the fusiformi-porrecto-ternate 

 ones are exceedingly long and slender, and are frequently 

 flexible near the attenuated base. An average sized 

 specimen which I measured was ith inch in length 

 and xnsth inch in its greatest diameter. The fusiformi- 

 recurvo-ternate spicula which occasionally accompany the 

 porrecto-ternate spicula average f^th inch in length, and 

 their greatest diameter was ^Jih. inch. The sarcode is 

 dense and semi-opaque, and abounds with the same minute 

 sigmoid bihamate spicula that are found in the dermal crust. 



There are two distinct sorts of gemmules in this sponge 

 which are always grouped together. The first is rather 

 the smaller of the two, and has a nucleus of slender 

 curved fusiformi-acerate spicula; only the bases of the 

 spicula cross each other at the centre of the gemmule, and 

 the apices radiate in all directions towards the external 

 surface, but do not in the fully- developed state of the 

 gemmule project beyond it. 



The second sort of gemmule is furnished with three 

 distinct forms of spiculum. The first are like those of 

 the gemmule described above, slender fusiformi-acerate, 

 the second are attenuato-porrecto-ternate, the radii being 

 given off from the apex, at about an angle of 45°; and 

 the third form is attenuato-bihamate or unihamate, and 

 the hooked apices of this form are projected further than 

 either of the other two forms, but do not pass beyond the 



